(a) Field of the Invention
This invention relates to a means for increasing the filling power of reconstituted tobacco by stiffening the tobacco by application of heat.
(b) State of the Art
Increasing the filling power of tobacco has long been recognized as desirable. To this end many processes have been suggested in the art.
Commonly, such processes involve subjecting tobacco to expansion treatments to increase its filling power. In such treatments the density of the tobacco is reduced and its filling power increased as a result of cell or pocket formation upon volatilization of a material trapped within the tobacco.
According to the expansion process described in U.S. Pat. No. 2,656,841, a cast film of gelantinized tobacco particles having a moisture content between 2 to 65%, is subjected to an intense heat such that the temperature of the film material is raised to 250.degree.-450.degree. F., most preferably 325.degree.-350.degree. F. The heat treatment may range from 0.1 to 5 seconds depending on the thickness of the film and its moisture content. As a result of this heat treatment the moisture becomes steam and pops or blisters the surface of the film, thereby forming pockets and reducing the density of the material.
Expansion processes of the above types are limited to tobacco forms in which the volatile materials can be confined so that their escape effects rupturing of the tobacco materials. However, reconstituted tobacco formed by conventional paper-making techniques, particularly that made without binder, generally lacks the structural integrity required to effect expansion according to such processes.
Reconstituted tobacco is commonly produced by forming a composition containing finely divided tobacco particles and a liquid, usually water, and drying the product, usually by heating. One common method of increasing the filling power of such reconstituted tobacco has been through foaming, as for example by introducing air into the slurry of tobacco parts before the forming step. This can give a significantly less dense product but one that is fragile and subject to breakage in further processing. The foaming operation is critical since the foam is subject to collapse and special equipment is required.
In U.S. Pat. No. 3,431,915 the filling power of reconstituted sheet is improved by stretching separated zones of sheet for a "creped" effect.
U.S. Pat. No. 3,194,245 describes a process for drying a cast sheet of a tobacco slurry containing 3-8% solids whereby the resulting reconstituted tobacco material has increased tensile strength and density. According to the method, the cast sheet is heated to 100.degree. C. to drive off the free water and thereafter to 120.degree.-160.degree. C.
It has now been discovered that by careful control of moisture content of reconstituted tobacco formed by conventional paper-making techniques, it is possible to substantially irreversibly increase its filling power by heat treatment for periods of time in excess of those required for simple moisture vaporization. The increase in filling power is effected by stiffening of the tobacco, rather than by cell or pocket formation.